I don't think there are varying degrees of genetic ability...
My cousin is that one guy in a crowd of a thousand that is immune to pepper spray. in his eye, mouth, whatever, it doesn't bother him. He's a cop. Has to be sprayed periodically.
My understanding of the process is that its like any thing else, over time, the nerves become less reactive to stimulus. Remove the stimulus for a time, and they begin to react again. SO if you want to be able to hang tough with the hottest peppers, get a supply of the hottest peppers, eat them, and continue to eat them frequently (daily maybe), and you'll be alright. No point in dragging out the conditioning process, its not like your tolerance is a muscle that can be over worked by running too far or something... Just hammer yourself with the hottest stuff you can find.
In short order it won't be that bad.
I grew up eating Jalapenos like candy. As an adult, I decided to eat habaneros. I bought some Hab based hot sauce and so forth... very quickly found my self not pushing my limit. After a trip to the UK, and to Peru where I ate a lot of hot stuff, I decided to grow some habs and other peppers to really stretch my limit. Bought a couple of plants from the big box, and started eating whole raw pods. The first time, I thought I'd die. the second time was bearable, in a week or two, habaneros are as spicy to me now as Jalapenos once were. Now I'm sucking down 7pots and so forth. If I had the 7pots to begin with, I'd have started there.